Point mutations in human Cu,Zn superoxide dismutase (HSOD) have been linked to the neurodegenerative disease amyotrophic lateral sclerosis (ALS), also known as Lou Gehrig's disease. ALS is a progressive paralytic disorder resulting from the degeneration of large motor neurons in the brain and spinal cord, and is usually fatal within five years of onset. We are probing the structural basis of this disease by determining the three-dimensional structures of several mutant HSODs. In conjunction with these structural studies, we are investigating the stability and functional properties of these mutant proteins to fully characterize their role in ALS.